This invention relates to a water-dispersible composition for coating articles with a polymer film.
It is highly desirable to provide a polymer film coating composition that is cold water dispersible. Those wishing to formulate pharmaceutical tablet coatings must either purchase each of the individual components and make their own formulation, or purchase a relatively dispersible coating composition which includes all or most of the ingredients in the tablet formulation. Putting a coating formulation together necessitates multiple weighings of ingredients and blending of same. Preparation of the coating requires dispersing the polymer into hot water with sufficient time required for cooling and hydration, or dispersing the polymer into room temperature water while under high shear conditions. In this latter method, additional time is required for the foam from shearing to subside. Otherwise, the polymer agglomerates, resulting in a dispersion which is not uniform and is therefore undesirable.
A dispersible powder coating disclosed in, Porter et al., U.S. Pat. No. 4,543,370, comprises hydroxypropyl methylcellulose, plasticizer, surfactant and optional pigments. When these ingredients are premixed dry and then added to room temperature water, due to the presence of the surfactant, the mixture's viscosity decreases. The formulated coating mixture disperses in water at room temperature and is usable about an hour after mixing.
A quantitative measurement of dispersibility in water can be generated by measuring the amount of agitation required to completely disperse the powders into water. The measure of agitation required for dispersion oan be rated on a scale of 0-10, 0 being minimal and 10 being violent agitation (see examples for test standards). Also, hydration time can be measured by a Brabender amylograph. Hydration is the time to achieve 90 percent of ultimate viscosity at a standard agitation level.
By measuring dispersibility and hydration, a dry powder mixture in room temperature water comprising hydroxypropyl methylcellulose, plasticizer and surfactant, which disperses at an agitation level of about 7 with a hydration time of 20 minutes. When pigments are added as taught in Porter et al, U.S. Pat. No. 4,543,370, allowing for better dispersibility, the agitation level drops to about 5 with a hydration time of less than 20 minutes.
It is known in the art to use dry powder mixtures in room temperature water as taught in U.S. Pat. No. 4,543,370, but these powder mixtures only have acceptable dispersion and hydration time in room temperature water. Thus, it would be highly desirable to formulate a cold water dispersible coating composition that is granular, with improved dispersibility and hydration time.